Aukey makes great chargers and portable battery banks, and the company's QC 3.0-compatible Dual USB car charger goes on sale somewhat frequently. Now you can get it from Amazon for just $9, once you use a promo code.
There's not much to explain about this charger, except that it has two USB ports and supports Qualcomm Quick Charge 3.0. So if you have one of the many QC-compatible devices, you'll be able to charge much faster than if you were using a standard car charger. Both ports support up to 2.4A of power output, so there isn't much (if any) slowdown when charging two devices at once.
You can find the charger at the source link below. You'll need to use the promo code 3YBPE635 at checkout to get the full discount.